This invention relates in general to photographic apparatus. More particularly it provides a film unit deflection system for use in self-developing cameras to control the distribution of a fluid photoprocessing composition within a self-processing film unit after a set of pressure-applying rollers initiate development of the film unit.
In self-processing film units of the type described in U.S. Pat. Nos. 3,415,644 and 3,594,165, a layer of a viscous fluid photoprocessing composition is spread over the exposed photosensitive surface to develop the image. The photoprocessing composition is typically held in a container at a forward edge of the film unit. The development process is initiated within the camera by passing the exposed film unit through the nip of a pair of pressure-applying rollers which rupture the container and spread the composition over the exposed photosensitive surface by a squeezing action.
Usually these film units are packaged in stacked relation in a film container or cassette that is conveniently loaded in the camera. To protect the film units from damage and exposure to light, the foremost film unit in the stack is covered by an opaque "dark slide" that is usually in the form of a rectangular piece of cardboard. The dark slide is stiffer than the film units and therefore exhibits a greater resistance to longitudinal bending than the film units. When the cassette is loaded in the camera, the dark slide is removed from the cassette in the same manner as the film units, that is, by advancement along a film processing path defined by the processing rollers, various film guide structures, and a film exit slot.
While the processing rollers are a generally effective arrangement for releasing and spreading the photoprocessing fluid over the photosensitive area of the film unit, the photoprocessing fluid tends to distribute in an uneven manner which detracts from the quality of the fully of the fully developed print. In particular, because the film unit is formed of flexible layers that are bound at their edges, the layer of photoprocessing fluid tends to be thicker at the central portions of the film unit than at its lateral portions and often fails to fill the trailing corners of the photosensitive area. Such voids result in dark, undeveloped corners on the resultant photograph.
On approach to solving these maldistribution problems described in U.S. Pat. Nos. 3,799,770 and 3,820,137, proposes that the film container and the camera, respectively, have structures for applying a secondary pressure to a central portion of the film unit to force the photoprocessing composition toward the edges of the film unit. Another prior solution is to influence the distribution of the composition by bending the film unit after it emerges from the processing rollers. For example, U.S. Pat. No. 3,810,211 describes a camera having a structure for inducing in the film unit a downward bend that places the upper flexible layer of the film under tension and the lower flexible layer under compression, and which thereby results in the desired distribution of the composition. In this camera, the deflecting structure is a plate which also acts as a light-shielding member.
In other self-developing camera, where the distance between the processing rollers and the exit slot is relatively short, (approximately 3/4 inch or 19.0 millimeters) an equivalent bending of the film unit is achieved by a smooth cam surface that deflects the film unit downwardly from the processing rollers to an exit slot. A commonly assigned, copending U.S. application Ser. No. 554,780, filed Mar. 3, 1975, now U.S. Pat. No. 3,994,002, by Andrew, S. Ivestor for "Self-Developing Camera with Film Unit Deflecting Structure" describes such a camming surface. It is also known to form a pair of raised areas on this camming surface that are aligned with the longitudinal edges of the film unit as described in the commonly assigned, copending U.S. application Ser. No. 648,672, filed Jan. 13, 1976, now U.S. Pat. No. 4,016,578, by the present applicant for "Photographic Film Processing Apparatus." These raised areas tend to enhance the distribution in a manner that reduces the likelihood of voids at the trailing corners of the film unit.
These fluid distribution arrangements, however, have been found to be unsatisfactory for use with certain photoprocessing compositions which are more viscous than conventional compositions, particularly at low temperatures which increase the viscosity of the composition. One way to properly distribute the more viscous composition is to increase the degree of bending of the film unit after it leaves the processing rollers. In cameras such as those marketed by the Polaroid Corporation under the registered designation SX-70, there is a sufficiently long distance between the rollers and the exit slot to accommodate this increased bending without adversely affecting other operations of the camera. In other cameras with more severe space limitations, such as the camera marketed by the Polaroid Corporation under the registered trade designation Pronto!, the necessary increase in bending can be achieved by a raised area or "bump" extending across the cam surface in a direction transverse to the direction of advance of the film units. When this modification in the cam surface is made, however, it has been found that the dark slide fails to eject from the camera with the desired degree of reliability and smoothness. This is because the dark slide is stiffer than the film units, and therefore requires an increased driving force to bend it toward the exit slot, but which can exceed the frictional engaging force between the processing rollers and the dark slide. As a result, the rollers tend to slip over the dark slide and it fails to eject. To correct this malfunction, it is necessary to open the camera and manually remove the dark slide. This is inconvenient, and is likely to expose one or more of the film units in the cassette.
It is therefore a principal object of this invention to provide a film unit deflection system for a self-developing camera and which produces a distribution of the process composition that covers the entire photosensitive area of the film unit, even at elevated viscosities associated with low temperatures, while at the same time not impeding the elimination of the dark slide from the camera.
Another object of the invention is to provide a deflection system which achieves the aforementioned advantages within a relatively short distance.
A further object of the invention is to provide a deflection system that is simple, has a relatively low cost of manufacture, and requires a minimum redesign of present camera structures.